Annular divided wall column for an air separation unit

ABSTRACT

An annular divided wall column for the cryogenic rectification of air or constituents of air is provided. The annular divided wall column includes a first annular column wall and a second annular column wall disposed within the first annular column wall to define an annulus column region and an interior core column region. The present annular divided wall column further includes structured packing elements disposed within at least the annulus column region as well as a ring-shaped cantilevered collector; and a ring-shaped distributor disposed in the annulus column region above or below the plurality of structured packing elements. The thermal expansion and contraction of the second annular column wall in a radial direction and in an axial direction is independent of the thermal expansion and contraction of the first annular column wall in the radial and axial directions.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of and priority to U.S.Provisional Patent Application Ser. No. 62/550,269 filed on Aug. 25,2017, the disclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to annular divided wall columns for thecryogenic rectification of air or constituents of air. Moreparticularly, the present invention relates to an annular divided wallcolumn that includes an annulus column region defined as the spacebetween a first annular column wall and a second annular column wall andan interior core column region defined as the interior space of thesecond annular column wall with a plurality of packing elements or traysdisposed within the interior core column region and the annulus columnregion.

BACKGROUND

A major capital expense of a rectification plant for the separation ofair into components based on their relative volatility is the cost ofthe column casing and the space required for the column. This isparticularly the case where two or more columns are required to conductthe separation. Such multi-column systems are often used in cryogenicrectification, such as in the cryogenic rectification of air, wherecolumns may be stacked vertically or located side by side. It would behighly desirable to have a system which will enable rectification to becarried out with reduced column cost and with reduced space requirementsfor the columns.

Divided-wall columns have been proposed in the literature as a means tobetter utilize a given column diameter, and thereby reduce the capitalcost associated with construction of a plant to facilitate theseparation process. Divided-wall columns essentially contain multipledistillation sections at the same elevation within a single columnshell. An early example of the use of a divided-wall column is disclosedin U.S. Pat. Nos. 5,946,942 and 6,023,945 (Wong, et al.) discloses anapplication of divided-wall principles to air separation. These priorart systems disclose an apparatus wherein the lower pressure columncontains an inner annular wall. The region contained between the innerannular wall and the outer shell of the lower pressure columnconstitutes a section for the production of argon product.

Drawbacks of the prior art divided-wall column systems include variousstructural and performance compromises made relating to designchallenges, including: (i) maldistribution of vapor within the differentsections of the divided wall column; (ii) maldistribution of thedown-flowing liquids due to the large wall surface areas, particularlywhere structured packing is employed as the mass-transfer elements;(iii) lower performance of the divided wall columns and column internalsdue to transient thermal expansion/contraction differences between theinner shell and outer shell; and (iv) inadequacy of a pressure boundarybetween the interior core column section and annulus column region ofthe annular divided wall columns.

Accordingly it is an object of this invention to provide an annulardivided wall column system for rectification of air which address theabove-identified design challenges and overcomes the difficulties anddisadvantages of the prior art annular divided wall columns to providebetter and more advantageous performance.

SUMMARY OF THE INVENTION

The present invention may be characterized as an annular divided wallcolumn for cryogenic rectification of air or constituents of air, saidcolumn comprising: (i) a first annular column wall; (ii) a secondannular column wall radially spaced from the first annular column walland disposed within a first interior space of the first annular columnwall to define an annulus column region between the first annular columnwall and the second annular column wall and to define an interior corecolumn region as part or all of a second interior space of the secondannular column wall; (iii) a conical shaped transition wall connected tothe second annular column wall proximate a top end of the second annularcolumn wall and further connected to the first annular column wall andconfigured to isolate the annulus column region from the interior corecolumn region proximate the top end of the second annular column wall;(iv) a plurality of structured packing elements or trays disposed withinthe interior core column region; and (v) a plurality of structuredpacking elements disposed within the annulus column region, whereinthermal expansion and contraction of the second annular column wall in aradial direction and in an axial direction is independent of the thermalexpansion and contraction of the [second] first annular column wall inthe radial direction and in the axial direction.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims distinctly pointing outthe subject matter that applicants regard as their invention, it isbelieved that the invention will be better understood when taken inconnection with the accompanying drawings in which:

FIG. 1 is a side section, cut-away view of a two-column divided wallarrangement in accordance with an embodiment of the present invention;

FIG. 2 is a side section, cut-away view of a two-column divided wallarrangement in accordance with another embodiment of the presentinvention;

FIG. 3 is a side section, cut-away view of an annular divided wallcolumn in accordance with one or more embodiments of the presentinvention;

FIG. 4 is a side section, cut-away view of an annular divided wallcolumn in accordance with still further embodiments of the presentinvention;

FIG. 5 is an isometric view of a ring tray suitable for use in one ormore embodiments of the present annular divided wall column;

FIG. 6 is an isometric view of a horseshoe tray suitable for use in oneor more embodiments of the present annular divided wall column;

FIG. 7 is an isometric view of a parallel flow tray suitable for use inone or more embodiments of the present annular divided wall column;

FIG. 8 is an isometric view of a two-pass crossflow tray suitable foruse in one or more embodiments of the present annular divided wallcolumn;

FIG. 9 is an isometric view of another two-pass crossflow tray suitablefor use in one or more embodiments of the present annular divided wallcolumn;

FIG. 10 is an isometric view of a two-pass parallel flow tray suitablefor use in one or more embodiments of the present annular divided wallcolumn;

FIG. 11 is an isometric view of a multiple downcomer tray suitable foruse in one or more embodiments of the present annular divided wallcolumn;

FIG. 12 is a isometric view of a type of arcuate wedge or curved packingsuitable for use in one or more embodiments of the present annulardivided wall column;

FIG. 13 is a partial isometric view of a section of the present annulardivided wall column showing the conical shaped transition wall andperforated plate;

FIG. 14 is a partial cross section view of a section of the presentannular divided wall column showing the conical shaped transition walland perforated plate after installation;

FIG. 15 depicts a partial cross section view of the present annulardivided wall column showing the conical shaped transition wall andperforated plate;

FIG. 16 is a partial isometric view of the present annular divided wallcolumn showing the structural support arrangement between the columnwalls with the pivoting arms and rolled angle ring;

FIG. 17 is a top view of the present annular divided wall column showingthe structural support arrangement between column walls with pivotingarms and rolled angle ring;

FIG. 18 is a close-up view of the pivoting arms and rolled angle ringconnecting the column walls in an embodiment of the present annulardivided wall column;

FIG. 19 is a partial isometric view of the ring-shaped support gridsuitable for use in embodiments of the present annular divided wallcolumn;

FIG. 20 is a top view of the of the ring-shaped support grid suitablefor use in embodiments of the present annular divided wall column;

FIG. 21 is a partial isometric view of the ring-shaped cantileveredcollector suitable for use in embodiments of the present annular dividedwall column;

FIG. 22 is a top view of the ring-shaped cantilevered collector suitablefor use in embodiments of the present annular divided wall column;

FIG. 23 is a partial cross section view of the ring-shaped cantileveredcollector;

FIG. 24 is a partial isometric view of the ring-shaped distributorsuitable for use in embodiments of the present annular divided wallcolumn; and

FIG. 25 is a top view of the ring-shaped distributor suitable for use inembodiments of the present annular divided wall column.

DETAILED DESCRIPTION

The following paragraphs include detailed descriptions of variousembodiments of the present annular divided wall column for the cryogenicrectification of air, including descriptions of: (i) annular dividedwall column configurations; (ii) process and/or service arrangements forthe different regions within the annular divided wall column; (iii)arrangements of mass transfer elements within the annular divided wallcolumn; (iv) annular divided wall column structural arrangements; (v)arrangements of collectors, distributors, and support structures withinthe annulus column region of the annular divided wall column; and (vi)flow distribution arrangements within the annular divided wall column.

Annular Divided Wall Column Configurations

As seen in the drawings, the first annular column wall 12 and the secondannular column wall 16 of the annular divided wall column 10 arepreferably concentrically disposed relative to one another as shown inFIGS. 1-4 Specifically, in FIG. 2 the annulus column region 114preferably contains structured packing 155 as well as the associatedcollectors 165, distributors 175, support structures, caps 190 andpiping while the interior core column region 118 also containsstructured packing and the associated collectors 135, distributors 145,support structures, caps and piping. The surface area density and/orgeometry of the structured packing in the annulus column region 114 maybe the same as or different than the surface area density and/orgeometry of the structured packing in the interior core column region118. In FIG. 1 the annulus column region 114 preferably contains aplurality of structured packing 155A, 155B as well as the associatedcollectors 165, distributors 175, support structures, caps 190, andpiping while the interior core column region 118 preferably includes aplurality of trays 150. Similarly, in FIG. 3 there are shown embodimentsof the annular divided wall column 10 wherein the annulus column region114 preferably contains structured packing 155A, 155B as well as theassociated collectors 165, distributors 175, support structures, caps190, and piping while the interior core column region 118 preferablyincludes a heat exchange device 120, a phase separator device and/or oneor more conduits for the movement of liquids and/or vapors within thecolumn. Lastly, in FIG. 4 the annulus column region 114 preferablycontains one or more beds of structured packing 155 as well as theassociated collectors 165, distributors 175, support structures, andpiping together with trays 180 while the interior core column region 118preferably contains both trays 150 and one or more beds of structuredpacking 125 as well as the associated collectors 135, distributors 145,support structures, caps, and piping.

In the illustrated embodiments of the two-column divided wallarrangement for the cryogenic rectification of air, the divided wallcolumn is preferably formed with two concentric annular column walls.The first annular column wall is preferably formed by the exterior shellof the air separation column structure such while the second annularcolumn wall extends over only a portion or section of the entireexterior column shell and is preferably disposed within the exteriorshell of the air separation column structure. In such two-column dividedwall arrangements, the vertical height of the first annular column wallis preferably greater than a vertical height of the second annularcolumn wall.

In the illustrated two-column divided wall arrangements, a cap or headermay be employed to partially enclose either the annulus column region orthe interior core column region. To partially enclose the annulus columnregion, a cap or header is placed above the annulus column region thatextends from the top of the second annular column wall to anintermediate location of the first annular column wall.

In some embodiments, it may be advantageous to apply a high flux coatingor porous coating to an interior surface of the first annular columnwall or third annular column wall. Similarly, a high flux coating orporous coating may also be applied to a surface of the second annularcolumn wall, preferably the surface exposed to the colder fluid. As usedherein, the terms ‘high-flux coating’ and ‘porous coating’ refers tothose coatings that by virtue of its built-in porosity enhance boilingby providing so-called nucleation sites. The porous coating providesmicro-scale cavities that have the effect of increasing the number ofnucleation sites and bubble departure frequency per site. As a result,the boiling rate can be enhanced. Examples of such high flux coatings orporous coatings are described in U.S. Patent Application PublicationNos. 2017/0108148 and 2017/0108296, the disclosures of which areincorporated by reference.

In other embodiments, the interior surface of the first annular columnwall, interior surface of the first annular column wall, or one or moresurfaces of the second annular column wall may also include surfacetexturing. The term “surface texturing”, as used herein, is to beunderstood as denoting any roughening, grooving, fluting, or otherwiseforming or impressing a geometric pattern on the wall surface.Preferably, if only one surface of the second annular column wall is tobe treated, the surface texture should be applied to the colder surfaceso as to enhance the boiling of liquid that may be trapped on the wall.

Process/Service Arrangements in an Annular Divided Wall Column

In some embodiments, the annulus column region is designed or configuredfor rectification of an argon-oxygen containing stream to separate theargon-oxygen containing stream into an argon-rich overhead stream and anoxygen-rich stream. In other embodiments, the annulus column region isdesigned or configured for rectification of a nitrogen-oxygen containingstream to separate the nitrogen-oxygen containing stream into a nitrogenrich overhead stream and an oxygen-rich stream.

Similarly, the interior core column region is designed or configured forrectification of an argon-oxygen containing stream to separate theargon-oxygen containing stream into an argon-rich overhead stream and anoxygen-rich stream. In other embodiments, the interior core columnregion is designed or configured for rectification of a nitrogen-oxygencontaining stream to separate the nitrogen-oxygen containing stream intoa nitrogen rich overhead stream and an oxygen-rich stream.

In yet other embodiments, the annulus column region may be designed orconfigured for rectification of a nitrogen-oxygen containing stream toseparate the nitrogen-oxygen containing stream into a first nitrogenrich overhead stream and a first oxygen-rich stream of a first purityand the interior core column region may be designed or configured forrectification of another nitrogen-oxygen containing stream to separateit into a second nitrogen rich overhead stream and a second oxygen-richstream of a second purity. Alternatively, the annulus column region maybe designed or configured for rectification of a nitrogen-oxygencontaining stream to separate the nitrogen-oxygen containing stream intoa first nitrogen rich overhead stream of a first purity and a firstoxygen-rich stream while the interior core column region may be designedor configured for rectification of another nitrogen-oxygen containingstream to separate it into a second nitrogen rich overhead stream of asecond purity and a second oxygen-rich stream.

Other contemplated process or service arrangements for the annulardivided wall column include disposing a heat exchange device or a phaseseparator device within the interior core column region. The heatexchange device disposed in the interior core column region ispreferably either: (i) an argon condenser configured to condense anargon-rich stream for use as a reflux stream, or a liquid argon productstream; (ii) a main condenser-reboiler configured to condense anitrogen-rich stream for use as a reflux stream or a liquid nitrogenproduct stream; or (iii) a subcooler configured to subcool anitrogen-rich liquid stream, an oxygen rich liquid stream, or a liquidair stream for use in the cryogenic air separation plant. In embodimentswhere a phase separator device is disposed in the interior core columnregion, the phase separator is preferably configured to separate atwo-phase oxygen-containing stream into an oxygen containing liquidstream and an oxygen containing vapor stream.

Mass Transfer Elements in an Annular Divided Wall Column

Turning now to FIGS. 5-11, the plurality of mass transfer contactingelements disposed within the interior core column region can be trays,packing or combinations thereof. Where trays are employed in theinterior core region of the annular divided wall column, suitable typesof trays include: ring trays 310 of the type generally shown in FIG. 5;horseshoe trays 320 of the type shown in FIG. 6; parallel flow trays 330of the type shown in FIG. 7; two pass crossflow trays 340 of the typeshown in FIG. 8 and FIG. 9; two pass parallel flow trays 350 of thetypes shown in FIG. 10; or multiple downcomer trays 360 of the typeshown in FIG. 11.

The preferred embodiments include structured packing in either theannulus column region and/or the interior core column region of theannular divided wall column, as such arrangements advantageously providelower pressure drop, higher efficiency, higher capacity; and reducedliquid hold-up compared to trays and random packing. However, structuredpacking is prone to liquid maldistribution. Structured packing isgenerally formed from corrugated sheets of perforated embossed metal orplastic, or wire gauze. The resulting structure is a very openhoneycomb-like structure with inclined flow channels of the corrugationsgiving a relatively high surface area but with very low resistance togas flow. In applications using structured packing, the structuredpacking is preferably constructed of materials selected from the groupconsisting of: aluminum sheet metal, stainless steel sheet metal,stainless steel gauze, and plastic. The surfaces of the structuredpacking may be smooth or may include surface texturing such as grooving,fluting, or patterned impressions on the surfaces of the structuredpacking sheets. Examples of the preferred types of structured packingare shown and described in U.S. Pat. Nos. 5,632,934 and 9,295,925; thedisclosures of which are incorporated by reference herein.

The size or configuration of structure packing is broadly defined by thesurface area density of the packing and the inclination angle of thecorrugated flow channels in the main mass transfer section of thestructured packing. The preferred density of the structured packing isbetween about 100 m²/m³ to 1200 m²/m³ and more preferably are selectedfrom the group of commercially available structured packing havingsurface area densities of 110 m²/m³; 220 m²/m³; 250 m²/m³; 350 m²/m³;430 m²/m³; 500 m²/m³; 730 m²/m³; 950 m²/m³; and 1200 m²/m³. The geometryof the structure packing, as characterized by the inclination angle ofthe corrugated flow channels in the main mass transfer section of thestructured packing, preferably includes a nominal inclination angle tothe horizontal axis of between about 35° to 70°, which encompasses thepreferred X-size packing (i.e. nominal inclination angle of about 60°),Y-size packing (i.e. nominal inclination angle of about 45°); and Z-sizepacking (i.e. nominal inclination angle of about 40°).

The preferred structured packing configuration for the annulus columnregion of the annular divided wall column are a plurality of curved orarcuate wedge shaped bricks 375 or curved bricks, shown in FIG. 12.Alternatively, the structured packing for the annulus column region maybe configured as a donut shaped disk or as conventional rectangularbricks. Although the curved or arcuate wedge shaped structured packingbricks can also be used in the interior core column region, thepreferred structured packing configuration for the interior core columnregion are round disks (e.g. pancake packing) or conventionalrectangular bricks. The preferred height of the disks and/or bricks isbetween about 10 inches and 12 inches, although half-height bricks of 5inches to 6 inches may also be used.

In some embodiments, a plurality of structured packing elements of afirst type are disposed within the annulus column region and a pluralityof structured packing elements of a second type are disposed within theinterior core column region, wherein the first type of structuredpacking elements and the second type of structured packing elements havedifferent surface area densities. For example, the structured packingelements disposed within the annulus column region (argon-oxygenseparation) may have a first surface area density whereas the structuredpacking elements disposed within the interior core column region(oxygen-nitrogen separation) may have different surface area densities.

In other embodiments, the structured packing elements in either theinterior core column region or the annulus column region may comprisetwo or more beds of structured packing. In addition, where multiple bedsof structured packing are employed in either region, the adjacent bedsmay have different surface area densities and/or different geometries.For example, a first bed of structured packing elements having a firstsurface area density may be disposed within the annulus column regionwhile a second bed structured packing elements having a second surfacearea density may be disposed within the annulus column region above orbelow the first bed of structured packing elements. In this example, thefirst bed of structured packing elements disposed within the annuluscolumn region may have a first surface area density whereas the secondbed of structured packing elements disposed within the annulus columnregion may have a different surface area density. Similarly, the firstbed of structured packing elements disposed within the annulus columnregion may have a first nominal inclination angle to the horizontal axiswhereas the second bed of structured packing elements disposed withinthe annulus column region may have a different nominal inclination angleto the horizontal axis.

Certain preferred embodiments employ a combination of structured packingelements and trays. For example, a plurality of structured packingelements may be disposed within the interior core column region and aplurality of trays is also disposed within the interior core columnregion above and/or below the structured packing elements. In suchembodiments, the structured packing elements disposed within theinterior core column region may have a surface area densities of betweenabout 100 m²/m³ to 1200 m²/m³ and a nominal inclination angle to thehorizontal axis of between about 35° to 70°, while the plurality oftrays may be selected from the group consisting of: ring trays;horseshoe trays; parallel flow trays; two pass crossflow trays; two passparallel flow trays; multiple downcomer trays; or combinations thereof.

Annular Divided Wall Column Structural Arrangements

As described above, the first annular column wall 512 and the secondannular column wall 516 are preferably concentrically disposed relativeto one another. More specifically, as shown in FIG. 13, FIG. 14, andFIG. 15 the second annular column wall 516 is hung from or otherwisemoveably attached to the first annular column wall 512 of thedistillation column 510 by way of a conical shaped transition wall 590that functions as the cap or header of the annulus column region 514. Asseen in figures, the conical shaped transition wall 590 is attached tothe second annular column wall 516 and extends from a location proximatethe top end of the second annular column wall 516 to an intermediatelocation of the first annular column wall 512. In this orientation, theconical shaped transition wall 590 is preferably disposed above andcovers or caps the annulus column region. In some embodiments, aseparate cap or header plate may also be used in conjunction with theconical shaped transition wall. The addition of a temporary plate 599 onthe bottom of the column as shown in FIG. 15 allows for independentpressure testing of the column section in the fabrication shop prior toinstallation to ensure there are no leaks between the two distillationprocesses in the annulus column region and in the interior core region.FIG. 15 also depicts a shipping support 585 for the column section to beused during transport of the column section from the fabrication site toinstallation site. While shown in FIGS. 13-15 as fixedly attached to thesecond annular column wall, the conical shaped transition wall 590 mayin some embodiments be removably connected to the second annular columnwall while also connected in a fixed or removable manner to the firstannular column wall.

In the illustrated embodiments, a ring shaped perforated plate 595 isalso disposed circumferentially around the second annular column walljust below the conical shaped transition wall 590. By using theperforated plate 595 and conical shaped transition wall 590, theascending vapor in the annulus column region 514 is forced to exit theannulus column region via a peripherally disposed outlet 597, whichminimizes the internal piping and manifolding typically used inconventional divided wall columns and thereby reducing the overalldistillation column height.

Proximate the lower end of the annulus column region 514, the secondannular column wall 516 is connected to and structurally supported bythe first annular column wall 512 of the distillation column 510 using aplurality of pivoting arms 598 that are disposed around the periphery ofthe second annular column wall 516 at a lower location as shown in FIGS.16-18. The exterior surface of lower section of the second annularcolumn wall 516 includes a rolled angle ring 592 which acts as astiffening support of the second annular column wall 516 allowingdifferential pressures between the interior column region 518 and theadjacent annulus column region 514. One end of each pivoting arm 598 isbolted or otherwise attached to the rolled angle ring 592 while theother end of each pivoting arm 598 is bolted or otherwise attached toone or more weld tabs 593 extending from the interior surface 594 of thefirst annular column wall 512.

Arranging and connecting the first annular column wall 512 and thesecond annular column wall 516 as described above provides two distinctadvantages. First, hanging the second annular column wall 516 from thefirst annular column wall 512 by way of the conical shaped transitionwall 590 and use of the pivoting arms 598 allows for radial and axialthermal expansion and contraction of the first annular column wall 512to be free relative to the radial and axial thermal expansion andcontraction of the second annular column wall 516. In other words, thethermal expansion and contraction of the second annular column wall 516in a radial direction and in an axial direction is independent of thethermal expansion and contraction of the first annular column wall 512in the radial direction and in the axial direction. Also, the connectingarrangements described above eliminates the need for the large andcumbersome inner shell support structures that are typically used inconventional annular divided wall columns thereby reducing the overallcolumn height.

Collectors, Distributors, and Support Structures within an AnnularDivided Wall Column

Turning now to FIG. 19 and FIG. 20, there is shown two views of aring-shaped support grid 600. The illustrated ring-shaped support grid600 has an inner annular edge member 602 and an outer annular edgemember 604 and is configured to support a plurality of structuredpacking elements in the annulus column region. The outer annular edgemember 604 is preferably attached to the first annular column wall whilethe inner annular edge member 602 remains unattached to the secondannular column wall during operation of the distillation column systemsuch that the thermal expansion and contraction of the second annularcolumn wall in a radial direction and in an axial direction isindependent of the thermal expansion and contraction of the ring-shapedsupport grid 600 and the first annular column wall in the radial andaxial directions.

In the illustrated embodiment, the ring-shaped support grid 600 furthercomprises a plurality of rigid bars 610 radially disposed around thering-shaped support grid 600 and connecting the outer annular edgemember and the inner annular support member. The ring-shaped supportgrid 600 further includes a plurality of primary arcuate support ribs612 and a plurality of secondary arcuate support ribs 614. Each of theprimary arcuate support ribs 612 have ends that are preferably attachedto different locations of the outer annular edge member 604 whereas eachof the secondary arcuate support ribs 614 have ends preferably attachedto other primary arcuate support ribs 612. The primary arcuate supportribs 612 may also be attached to the radial bars 610.

Turning now to FIG. 21, FIG. 22, and FIG. 23, there are shown differentviews of a ring-shaped cantilevered collector 700 configured to beplaced in the annulus column region 514 above or below the plurality ofstructured packing elements. As seen most clearly in FIG. 23, thering-shaped cantilevered collector 700 is preferably rigidly attached toone of the first annular column wall 512 or second annular column wall516 and extends radially toward the other annular column wall around theentire circumference of the annulus column region 514. As shown in theFigures, the ring-shaped collector 700 includes a first collector wall702, a second collector wall 704 and a collector deck 706 extendingtherebetween. The first collector wall 702 is configured to be attachedto the first annular column wall 512 with the first collector wall 702having a bottom support ring 708 and a tapered top edge 710 thatfacilitates transfer of descending liquid on the interior surface 594 ofthe first annular column wall 512 to the collector. The second collectorwall 704 is configured to be arranged proximate the second annularcolumn wall 516 but remains unattached to second annular column wall 516thus defining the ring-shaped cantilevered collector 700. The collectordeck 706 is attached to the support ring 708 of the first collector wall702 and the second collector wall 704. The ring-shaped cantileveredcollector 700 also includes one or more sumps 715 disposed in thecollector deck 706 and circumferentially spaced around the collectordeck. Downcomers 724 are connected to the one or more sumps and areconfigured to receive the liquid from the one or more sumps and directsuch liquid to a liquid distributor disposed below the ring-shapedcantilevered collector.

The ring-shaped cantilevered collector 700 further includes a pluralityof arcuate vapor risers 720 extending upwards from the collector deck706 and configured to allow the ascending vapor in the annulus columnregion to rise through the ring-shaped cantilevered collector 700. Theplurality of arcuate vapor risers 720 are disposed in a generalring-shaped pattern around the collector deck 706 and define liquidcollection channels on the collector deck. On top of each of the vaporrisers 720 is a cover or hat 722 that collects descending liquid thatwould otherwise fall into the interior space of the vapor riser. Theliquid collected in the covers or hats 722 are channeled towards the oneor more sumps or the liquid collection channels.

Since the ring-shaped cantilevered collector 700 is only rigidlyattached to one of the annular column walls, the differing thermalexpansion/contraction of the first and second annular column walls in aradial direction and/or in an axial direction does not adversely impactthe performance of the liquid collector or the distillation occurring inthe annulus column region.

FIG. 24 and FIG. 25 show views of a ring-shaped distributor 800configured to be placed in the annulus column region above a bed of thestructured packing elements. The ring-shaped distributor 800 includes aplurality of pre-distribution boxes 802 configured to couple thering-shaped distributor to the downcomers 724 of the ring-shapedcollector 700 of the type described with reference to FIGS. 21-23.Although pan type distributors may be used, the illustrated ring-shapeddistributor 800 is a trough type liquid distributor that includes anannular distributor channel 804 configured for distributing the liquidreceived from the collector via the pre-distribution boxes 802 in agenerally circular pattern and plurality of troughs 801 disposed on eachside of the annular distributor channel 804 and configured fordistributing the liquid from the annular distributor channel to thestructure packing bed immediately below the ring-shaped distributor 800via apertures on the bottom surface of the troughs. The annulardistributor channel also includes a plurality of apertures 805 fordistributing a portion of the liquid to the surfaces of the structuredpacking elements directly below annular distributor channel 804.

The ring-shaped distributor 800 further includes a ring-shaped supportbase 810 configured to support the annular distributor channel 804 andplurality of troughs 801. A pair of annular support rings 815 are alsodisposed on top of the plurality of troughs 801 and attached thereto tosupport the pre-distribution boxes 802 and keep the plurality of troughsand annular distributor channel in the general ring-shapedconfiguration. There are also shown a plurality of stiffening structures818 or arms extending between the pair of annular support rings also tokeep the plurality of troughs and annular distributor channel in thegeneral ring-shaped configuration. The plurality of troughs 801 arefurther arranged to allow ascending vapor from the structure packing bedimmediately below the ring-shaped distributor 800 to flow upward betweenadjacent troughs and through the ring-shaped distributor.

As with other trough type liquid distributors, the distributors are hungfrom one or more support beams 820. In the illustrated embodiments, aplurality of support beams 820 are attached to the annular support ringsand/or the plurality of troughs. The plurality of support beams 820 haveone or both ends that are bolted or otherwise attached to one or moreweld tabs extending from the interior surface of the first annularcolumn wall (i.e. outer shell of the annulus column region) via one ormore sliding clips. Again, since the ring-shaped distributor is onlyrigidly attached to the first annular column wall and not to the secondannular column wall, the differing thermal expansion and contraction ofthe annular column walls in a radial direction and/or in an axialdirection do not adversely impact the performance of the liquiddistribution or the overall distillation occurring in the annulus columnregion. In addition, the ring-shaped distributor as well as thering-shaped collector and may also be supported by a specially designedsupport plate that is attached to the column walls or that restsdirectly on the structured packing.

Uniform Flow Distribution within the Annular Divided Wall Column

When designing the present annular divided wall column arrangements, akey design challenge is to ensure the arrangement achieves the desiredascending vapor split between the annulus column region and the interiorcore column region. In other words, the correct amount of ascendingvapor must be directed to both the annulus column region and to theinterior core column region. If the desired ascending vapor split ratiobetween the annulus column region and the interior core column region isnot the same as the ratio of the cross section areas of the annuluscolumn region to the interior core column region, adjustments to thevapor split should be considered. One such preferred adjustment is tovary the design of the collectors. For example, by varying or adjustingthe open area for vapor flow in the lowermost collector at the bottom ofthe annulus column region and the open area for vapor flow lowermostcollector at the bottom of the interior core column regions so that itis proportional to the desired vapor split.

Another key design challenge is to ensure that the vapor and liquidbeing fed into the annulus column region is uniformly distributed aroundand across the annulus. The preferred structure and method to addressthis design challenge is to provide a symmetrical arrangement of thefeed piping (inlet) and, to a lesser extent, the draw piping (outlet).In the presently disclosed embodiments, each feed piping (inlet)arrangement includes two or more feeds together with the use ofhorseshoe shaped sparger feed pipes that traverse around the annulus ina circular shape.

In addition, higher pour point densities may be needed or desired forthe ring-shaped liquid distributors in the annulus column regioncompared to the pour point densities for the liquid distributors in theinterior core column region to counteract higher susceptibility to wallflow in the annulus column region due to more wall area.

While the present inventions have been characterized in various ways anddescribed in relation to the preferred structural embodiments and/orpreferred methods, there are numerous additions, changes andmodifications that can be made to the disclosed structures and methodswithout departing from the spirit and scope of the present invention asset forth in the appended claims. For example, while the present annulardivided wall column has been shown and described as suitable for use inthe cryogenic rectification of air or constituents of air in an airseparation unit, it is fully contemplated that such annular divided wallcolumn arrangements may also be suitable for the separation orpurification of other industrial gases including off-gases or tail gasesof various industrial processes.

We claim:
 1. An annular divided wall column for cryogenic rectificationof air or constituents of air, said column comprising: a first annularcolumn wall; a second annular column wall radially spaced from the firstannular column wall and disposed within a first interior space of thefirst annular column wall to define an annulus column region between thefirst annular column wall and the second annular column wall and todefine an interior core column region as part or all of a secondinterior space of the second annular column wall; a conical shapedtransition wall connected to the second annular column wall proximate atop end of the second annular column wall and further connected to thefirst annular column wall and configured to isolate the annulus columnregion from the interior core column region proximate the top end of thesecond annular column wall; a plurality of structured packing elementsof a first type or trays disposed within the interior core columnregion; and a plurality of structured packing elements of a second typedisposed within the annulus column region; wherein the conical shapedtransition wall is either: (i) fixedly attached to the second annularcolumn wall proximate the top end of the second annular column wall andmoveably hung on the first annular column wall; or (ii) moveablyconnected to the second annular column wall proximate the top end of thesecond annular column wall and fixedly connected to the first annularcolumn wall; and wherein thermal expansion and contraction of the secondannular column wall in a radial direction and in an axial direction isindependent of the thermal expansion and contraction of the firstannular column wall in the radial direction and in the axial direction.2. The annular divided wall column of claim 1, wherein a vertical heightof the first annular column wall is greater than a vertical height ofthe second annular column wall.
 3. The annular divided wall column ofclaim 1, wherein the annulus column region is configured forrectification of an argon-oxygen containing stream to separate it intoan argon-rich overhead stream and an oxygen-rich stream.
 4. The annulardivided wall column of claim 1, wherein the annulus column region isconfigured for rectification of a nitrogen-oxygen containing stream toseparate it into a nitrogen rich overhead stream and an oxygen-richstream.
 5. The annular divided wall column of claim 1, wherein theinterior core column region is configured for rectification of anargon-oxygen containing stream to separate it into an argon-richoverhead stream and an oxygen-rich stream.
 6. The annular divided wallcolumn of claim 1, wherein the interior core column region is configuredfor rectification of a nitrogen-oxygen containing stream to separate itinto a nitrogen rich overhead stream and an oxygen-rich stream.
 7. Theannular divided wall column of claim 1, wherein the annulus columnregion is configured for rectification of a nitrogen-oxygen containingstream to separate it into a first nitrogen rich overhead stream and afirst oxygen-rich stream of a first purity and the interior core columnregion is configured for rectification of the nitrogen-oxygen containingstream to separate it into a second nitrogen rich overhead stream and asecond oxygen-rich stream of a second purity.
 8. The annular dividedwall column of claim 1, wherein the annulus column region is configuredfor rectification of a nitrogen-oxygen containing stream to separate itinto a first nitrogen rich overhead stream of a first purity and a firstoxygen-rich stream and the interior core column region is configured forrectification of the nitrogen-oxygen containing stream to separate itinto a second nitrogen rich overhead stream of a second purity and asecond oxygen-rich stream.
 9. The annular divided wall column of claim1, wherein the plurality of structured packing elements are constructedof materials selected from a group consisting of: aluminum sheet metal,stainless steel sheet metal, stainless steel gauze, silicon carbide; andplastic.
 10. The annular divided wall column of claim 1, wherein theplurality of structured packing elements of a first type are disposedwithin the annulus column region and the plurality of structured packingelements of a second type are disposed within the interior core columnregion; wherein the first type of structured packing elements and thesecond type of structured packing elements have different surface areadensities.
 11. The annular divided wall column of claim 10, wherein theplurality of structured packing elements of the first type and of thesecond type have a surface area density between about 100 m²/m³ to 1200m²/m³.
 12. The annular divided wall column of claim 1, wherein theplurality of structured packing elements of a first type are disposedwithin the annulus column region and the plurality of structured packingelements of a second type are disposed within the interior core columnregion; wherein the first type of structured packing elements and thesecond type of structured packing elements have different geometries.13. The annular divided wall column of claim 12, wherein the pluralityof structured packing elements have a geometry that includes a nominalinclination angle of corrugations to the horizontal axis of betweenabout 35° to 70°.
 14. The annular divided wall column of claim 1,wherein the plurality of structured packing elements are configured asrectangular bricks or arcuate shaped wedges.